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May 2008

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Subject:
Re: Methodology for determining the # of reworks ENIG finished solder lands for leaded components can withstand
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 23 May 2008 15:57:03 EDT
Content-Type:
text/plain
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text/plain (42 lines) 
Hi Joe,
I'll give you a non-Friday answer—and, unfortunately, or fortunately from my 
consultant-perspective, it does depend.
What it depends on is the amount of P enrichment you get at the interface 
after each rework cycle. The P-concentration in the ENi has to be high enough to 
prevent hyper-galvanic corrosion at the Ni grain boundaries during 
imAu-plating, but low enough to prevent 'Black Pad', which is characterized by en 
enrichment of P at the interface. Because every rework cycle dissolves more Ni, more 
P is left behind weakening the adhesive strength of that interface.
The good news is youare likely able to get more rework cycles than when 
soldering to Cu, since Cu dissolces much faster than ENi.

Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, June 17, London
Interconnect Failures and Design for Reliability for PCB PTHs, June 17, 
London
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18, 
Orlando
Reliability Issues with Lead-Free Soldering Processes, September 22, 
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 
ENIG), September 22, Schaumburg



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